1. Field of the Invention
The present invention relates to a semiconductor chip including a plurality of processing devices such as processor elements or the like.
2. Description of the Related Art
A semiconductor chip including a plurality of identical processor elements (Processing Elements: PE) is known.
Each PE includes an arithmetic unit (core), an individual memory (LS: Local Storage) connected to the core on a one-to-one basis, and a communication unit (COM) for performing communication with another PE.
Techniques of using the individual memory (LS) of an unused core between PEs, or lending and borrowing the LS of a core between PEs in such a semiconductor system are proposed (see “NGARC Forum 2007 Kyushu University, Memory Architecture of Next-Generation Multiprocessor,” for example).
In addition, techniques of turning off power to the whole of a PE by a power gate (PG) are known (see Japanese Patent No. 3899092, for example).
FIGS. 1A, 1B, and 1C are diagrams showing an example of a configuration when the techniques of a power gate are applied to the proposed techniques of lending and borrowing the LS of a core between PEs.
In the example of FIG. 1, two PEs, that is, a PE-a and a PE-b are connected to a power supply potential Vcc and configured such that an LS can be lent and borrowed between the PE-a and the PE-b.
The PE-a includes a core 1a, an LS 2a of the core 1a, and a communication unit (COM) 3a. Then, the PE-a has a power control unit 4a formed by a power gate that is connected between the power supply terminal of the PE-a as a whole and the power supply potential Vcc and which can turn on and off the power supply line.
The PE-b includes a core 1b, an LS 2b of the core 1b, and a communication unit (COM) 3b. Then, the PE-b has a power control unit 4b formed by a power gate that is connected between the power supply terminal of the PE-b as a whole and the power supply potential Vcc and which can turn on and off the power supply line.
The communication unit 3a of the PE-a and the communication unit 3b of the PE-b are connected to each other.
As shown in FIG. 1A, when both of the PE-a and the PE-b are operated, the PE-a and the PE-b are both maintained in an on state (operating state) by the power control units 4a and 4b. 
As shown in FIG. 1B, when only the PE-a is operated, the PE-a is maintained in the on state (operating state) by the power control unit 4a, and the PE-b is maintained in an off state (non-operating state) by the power control unit 4b. 
As shown in FIG. 1C, when the PE-a operates and the PE-a uses the LS 2b of the PE-b, that is, the PE-a borrows the LS 2b of the PE-b (the PE-b lends the LS 2b to the PE-a), the PE-a and the PE-b are both maintained in the on state by the power control units 4a and 4b. 